Fine dispersion aluminum base bearing

ABSTRACT

A mixture of metals composed predominantly of aluminum and the balance bearing phase materials are heated to a molten state, ejected through an orifice and atomized by impinging a stream of cold water against the molten metal to effect a rapid drop in temperature as well as solidifcation. A layer of the resulting pre-alloyed particles are roll compacted simultaneously with a sacrificial surface layer and a bottom bonding layer, both being composed of aluminum base particulate materials. The bottom layer is devoid of bearing phase materials. The tri-layer strip is sintered, roll clad onto a backing member and post-annealed, blanked and formed into a bearing which is bored to remove the sacrificial layer.

This application is a continuation of application Ser. No. 98,233, filedDec. 15, 1970 which in turn is a continuation-in-part of applicationSer. No. 704,678, filed Feb. 12, 1968, and both now abandoned.

The present invention relates generally to an aluminum base bearing forautomotive applications made by powder metallurgy techniques and, moreparticularly, to a bearing having a surface layer of pre-alloyed,aluminum base particles.

In the prior art aluminum base bearings made by powder metallurgytechniques containing a bearing phase of conventional materials such aslead, tin, cadmium, etc., are already known in the art. Considerabledifficulty has been experienced in the fabrication and use of suchbearings. Essentially, the problems reside in the difficulty to impartadequate bearing load carrying capacity and anti-seizure properties tothe bearing structure. The absence of such properties causes cracking ofthe grain interparticle boundary and a pull out of the bearing phaseparticles from the bearing surface. In conventional aluminum basebearings produced by powder metallurgy techniques, the bearing phaseparticles have an interstitial position relative to the aluminumparticles and, consequently, the bearing phase distribution issignificantly coarse. In producing aluminum-lead-tin type bearings byroll compacting the difficulty of processing such a structure isincreased due to the interaction between the bearing phase, and thecontact surfaces of the rolling mills which causes considerableadherence of particles of the compacted strip to the bonding roll.

It has now been found that the difficulties experienced with the priorart bearings and the method for making same can be obviated by a bearinglayer in which the particles of the bearing layer are predominantly inpre-alloyed powder form and particularly the bearing phase is in anintra-particle position relative to the aluminum. In conventionalaluminum base bearings the bearing phase is in an inter-particleposition relative to the aluminum. The invention thus provides a bearingsurface in which an interstitial position of the bearing phase betweenthe aluminum particles is prevented and a fine dispersion of the bearingphase in each individual aluminum particle is established.

The distinction between the inter and intra-particle position of thealuminum and a bearing phase is of fundamental importance. When suchbearing phase particles are used in elemental form they have a tendencyto interfere with the bond between the aluminum particles. This is atleast in part due to the interposition of such particles between thealuminum. Even the use of only 10 to 15% of some bearing phase materialin elemental form has been found to have deleterious effects. Tri-layeraluminum base type powder metal bearings as such have been known alreadyfor some time. For instance, see British Pat. No. 773,722. However, suchbearings have a surface layer of bearing phase particles in elementalform and are therefore believed to lack the strength required forautomotive applications.

In order to overcome the difficulties normally encountered during rollcompacting and roll cladding of the bearing strip having a finedispersion of the bearing materials, a sacrificial and temporary layerof intermixed particles predominantly of aluminum and bearing phasematerials is utilized. The sacrificial layer is removed afterfabrication of the strip or bearing.

It is also well known in the prior art that considerable bondingproblems occur with respect to aluminum base materials containingbearing phase additives, when such materials are roll clad onto a steelbacking member which is commonly used to provide the strength requiredfor a bearing. The layer of pre-alloyed aluminum base powder, producedin accordance with this invention, is powder rolled simultaneously witha layer of aluminum base or pure aluminum particulate material. Thislast mentioned layer is thus metallurgically compatible with the steelbacking member due to the absence of bearing phase materials and cantherefore be directly bonded to the steel member. Furthermore, anintermingling of the particles of the bonding layer with those of thepre-alloyed layer establishes a transition zone of considerable depthand consequently promotes a strong bond between the layers.

As used herein "interstitial" position of the bearing phase is definedas the condition in the consolidated aggregate which has the bearingphase completely surrounded by aluminum particle regions. The boundariesof the separate original particles, i.e., bearing phase and aluminumphase particles, are discernible and intact in the final product.

It is therefore the primary object of this invention to provide abearing strip and bearing for automotive applications of aluminum basepowder particles which avoids the difficulties described above andnormally experienced with articles known in the prior art and in whichthe surface layer is composed of aluminum base particles containing afine dispersion of a bearing phase.

It is another object of this invention to provide, by powder metallurgy,an aluminum base anti-friction bearing and bearing strip having highfatigue as well as excellent anti-seizure properties.

An aspect of the present invention resides in the provision of a finedispersion aluminum base anti-friction bearing, for automotive use,which is composed of a steel backing member and a powder metal bondinglayer on the backing layer comprising more than 55 weight percentaluminum and the balance selected from a first group of additivematerial consisting of silicon, copper, manganese, magnesium, nickel,iron, zinc, chromium, zirconium and titanium. A powder metal bearinglayer is provided on the bonding layer and consists essentially of atleast 55 weight percent aluminum and the balance selected from the abovementioned first group of material in an amount of 0 to about 20 weightpercent and from a second group composed of bearing phase materials inthe amount of 5 to 25 weight percent. The second group consists of lead,tin, cadmium, bismuth and antimony. At least all of the aluminum and thebearing phase material(s) of the bearing layer being in pre-alloyedparticle form to establish an intra-particle position relative to eachother.

A further aspect of the present invention resides in the provision of amethod for making a bearing strip for automotive bearings, in which thesteps include the heating of a mixture of metals which are predominantlyaluminum and the balance comprised of lead, tin and cadmium or otherbearing phase materials. These metals are heated to a molten state andare atomized to achieve a rapid drop in temperature and solidificationof the now pre-alloyed particles. These particles are then rollcompacted as a layer simultaneously with and interposed between twoother layers of aluminum base particles. The tri-layer is sintered andthe bottom layer thereof is roll clad onto a steel backing member andthereafter the surface layer is removed.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

In the drawings:

FIG. 1 is a diagrammatic view illustrating a continuous production linefor producing a bearing strip and a bearing in accordance with thisinvention;

FIG. 2 is a schematic illustration of an aluminum base particle inaccordance with this invention;

FIG. 3 is a schematic illustration showing an interstitial position of abearing phase material surrounded by particles of aluminum;

FIG. 4 is a perspective view of a conventional and typical bearingstructure; and

FIG. 5 is a typical cross-section of the final bearing.

Referring now to the drawing and particularly FIG. 1 thereof, there isshown a crucible 10 for pre-alloying aluminum base particles 12. The rawmaterial 12 is either in ingot or particle form and may be a mixture ofelemental constituents, a mixture of elemental and alloyed material or amixture of alloys. The raw material 12 is placed into the crucible 10and is heated and vigorously stirred therein for several minutes at atemperature of about 1800° to 1900° F. to melt the individualconstituents until the melt has been reduced to a single liquid phase. Amelting process of this type is described, in greater detail, in U.S.Pat. No. 1,959,029. The crucible 10 is provided with an orifice 14 toeject the molten mass, under pressure, in a continuous stream 16. Waterat room temperature, or air, impinges upon the stream of molten mass 16to disintegrate the stream and to atomize the molten mass andsimultaneously to solidify the resulting particles. The water isdirected by means of a jet 18 against the molten mass 16 in such amanner so that the resulting fine drops, or particles, fall into and arecollected by a drum 20. Suitable provision is made (not shown) to drainthe water. Also, as an alternate to water, gas other than air may beutilized to disintegrate the molten stream 16.

Each of the resulting powder particles 22 is composed of aluminum, abearing phase material and, optionally, an additive material as moreparticularly delineated in the Table shown below. The bearing phase (bp)is uniformly dispersed through each aluminum base particle (Al) asschematically shown in FIG. 2. This may be compared to a conventionalbearing structure which is obtained by compacting intermixed aluminum(Al) and bearing phase (bp) powders and in which an interstitialposition of the bearing phase is established in the final product eventhough full consolidation of the aggregate is obtained; for illustrativepurposes, such a structure is shown in FIG. 3. Consequently, thepre-alloyed aluminum base constituents in accordance with this inventionhave an intra-particle bearing phase dispersion, see FIG. 2, whereas thestructure in accordance with the prior art has an inter-particle bearingphase distribution, see FIG. 3. The additives described in the Table canbe dispersed in each individual particle or provided in elemental form,although the former approach is preferred.

Each individual particle of aluminum base pre-alloyed material iselongated in the direction of rolling. The bearing phase, however, whilefinely and uniformly dispersed in each particle, is only slightlyelongated. A typical pre-alloyed aluminum base powder particle in thefinal structure is, in the preferred embodiment, about 100 microns longand about 40 microns in width and thickness. The average distanceseparating the bearing phase within a single particle is approximately 5microns.

The pre-alloyed particles 22 are then collected and dried and fabricatedinto a bearing strip by being placed into the center opening of a hopper24 to the left side of which (in the drawing) there is placed aluminumbase powder particles 26 to form a bottom or bonding layer, and to theright of layer 22 there is placed a quantity of aluminum base powderparticles 28 with bearing phase particles intermixed to establish asacrificial surface layer to facilitate the roll compacting of thealuminum particles 22. The bonding layer particles 26 are made ofmaterials devoid of a bearing phase to prevent roll sticking of thepre-alloyed materials 22 and to provide a suitable bonding surface. Thealuminum base materials 26 and 28 are selected in such a manner to avoidroll sticking, as already noted above, and to establish a closelyrelated, or identical, coefficient of friction with the rolls 30 toprovide substantially equal powder feed between the rolls.

For most bearing applications the bearing layer 22 is composed ofsubstantially only pre-alloyed particles. However, for some specialapplications, it is possible to use the pre-alloyed particles withparticles of additive material in elemental form. This may beaccomplished by solidifying a multi-phase liquid solution. In any event,however, at least all of the aluminum and bearing phase material of thebearing layer are in a pre-alloyed particle state so as to establish anintra-particle position relative to each other. The bearing layer 22 asa whole should not contain more than a total of 20 weight percentadditives (as listed in the Table) of the total composition, and theadditives together with the bearing phase should not exceed 45 weightpercent. Consequently, the bearing layer is composed of at least 80weight percent pre-alloyed particles (aluminum and bearing phase),although, preferably, close to 100 weight percent.

In the preferred embodiment, the bonding layer is essentially composedof pure aluminum. Alternatively, however, at least 55 weight percent ofaluminum may be utilized with the balance being composed of materialsother than those normally classified as bearing materials, see Table.The particles of layer 26 may be either in elemental or alloyed form.

The particles 28 of the sacrificial layer, in the preferred embodiment,are also predominantly composed of aluminum with the balance comprisingintermixed additives and bearing phase material in either elemental oralloyed form, so that the bearing phase particles have an interstitialposition relative to said aluminum particles.

The following Table shows the composition of the three layers in greaterdetail.

    __________________________________________________________________________    COMPOSITION                                                                   (In Weight Percent)                                                                   Base                                                                          Mat.                                                                             Additives             Bearing Phase                                        Al Si                                                                              Cu                                                                              Mn Mg Ni                                                                              Fe                                                                              Zn                                                                              Cr                                                                              Zr                                                                              Ti                                                                              Sn                                                                              Pb                                                                              Cd                                                                              Bi                                                                              Sb                                   __________________________________________________________________________    Bonding                                                                            Min                                                                              55 0 0 0  0  0 0 0 0 0 0 --                                                                              --                                                                              --                                                                              --                                                                              --                                   Layer                                                                         (26) Max                                                                              100                                                                              13                                                                              7 1.5                                                                              6  3 2 8 1 1 1 --                                                                              --                                                                              --                                                                              --                                                                              --                                   Bearing                                                                            Min                                                                              55 0 0 0  0  0 0 0 0 0 0 5 5 5 5 5                                    Layer                                                                         (22) Max                                                                              95 13                                                                              7 1.5                                                                              6  3 2 8 1 1 1 25                                                                              25                                                                              25                                                                              25                                                                              25                                   Sacri-                                                                             Min                                                                              50 0 0 0  0  0 0 0 0 0 0 0 0 0 0 0                                    ficial                                                                        Layer                                                                              Max                                                                              98 13                                                                              7 1.5                                                                              6  3 2 8 1 1 1 50                                                                              50                                                                              50                                                                              50                                                                              50                                   (28)                                                                          __________________________________________________________________________

The powder particles 22, 26 and 28 are then passed through the powderroll mill 30 and are densely compacted. The resulting tri-layer issintered in two stages in sintering furnace 32. The initial hold in thefurnace 32 is for about two hours at 400° F. and is designed to permitthe gas within the composite to escape to avoid the formation ofbubbles. Thereafter the temperature in the sintering furnace 32 isincreased to 600° to 1100° F. for sintering the tri-layer. The exacttemperature and time varies depending upon the internal structuredesired. For example, sintering at about 650° F. for 1/2 hour has beenfound to be satisfactory.

The sintered structure is then passed through rolls 34 to roll clad asteel backing member 36, face to face, onto the bonding layer 26.Depending upon the ultimate use of the bearing material, the resultingstructure is optionally post-annealed for about 30 minutes in anannealing furnace 38 having a temperature of about 600°-750° F.

The strip composed of powder particles 28, 22 and 26 and backing member36 is then blanked and formed into a bearing of conventional shape, bymeans of conventional bearing fabrication techniques, as shown forpurposes of illustration in FIG. 4.

The bearing structure resulting from the aforedescribed process is shownin cross section in FIG. 5. Each aluminum base layer is identified bythe numeral denoting the particle of which each layer is composed.

In order to expose the bearing layer 22, the bearing B, see FIG. 4, isbored by conventional means to suitable dimensions and until all of thelayer 28 has been removed. This process step may optionally be performedbefore the blanking of the bearing strip.

While the most economic and preferred way of carrying out the inventionhas been described above, it is, however, possible to modify thecomposition of the bonding layer, for instance by incorporating into thelayer a bearing phase which is not normally compatible, for bondingpurposes, with the steel backing member. In such a case, in accordancewith conventional practices, the backing member must be coated with abonding interlayer, such as a nickel flash, in order to assure adhesionof the multi-layer aluminum base structure to the backing member.

The following are typical examples of the composition of each aluminumbase layer in accordance with this invention.

Bonding Layer 26:

1. 100% aluminum (commercial purity).

2. 94% aluminum and 6% silicon.

3. 0.8% silicon, 4.4% copper, 0.8% manganese, 0.4% magnesium, and thebalance aluminum.

Bearing Layer 22:

1. 8.5% lead, 1.5% tin, 4% silicon, 1% copper, and the balance aluminum.

2. 17% lead, 3% tin, 1% copper and the balance aluminum.

3. 20% tin, 1% copper and the balance aluminum.

Sacrificial Layer 28:

1. 20% tin, 1% copper and the balance aluminum.

2. 20% lead and the balance aluminum.

3. 17% lead, 3% tin and the balance aluminum.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:
 1. A sintered, coherent, multi-layer powder metalcomposite comprising a powder metal bonding layer, a powder metalbearing layer strongly bonded to said powder metal bonding layer by asintered transition zone of compacted, intermingled powder particles ofsaid bearing layer and said bonding layer, and a powder metalsacrificial layer bonded to said powder metal bearing layer by asintered transition zone of compacted, intermingled powder particles ofsaid bearing layer and said sacrificial layer,said powder metal bondinglayer comprising more than 55 weight percent aluminum and the balancematerial selected from a first group of additives consisting of silicon,copper, manganese, magnesium, nickel, iron, zinc, chromium, zirconium,titanium and mixtures thereof; said powder metal bearing layercomprising from 55 to about 95 weight percent aluminum, from 5 to 25weight percent bearing phase material selected from a second group ofadditives consisting of lead, tin, cadmium, bismuth, antimony andmixtures thereof, and from 0 to about 20 weight percent materialselected from said first group of additives, at least all of saidaluminum and said bearing phase material of said bearing layer being inpre-alloyed particle form with said bearing phase material dispersed inan intra-particle position relative to said aluminum; said powder metalsacrificial layer comprising intermixed aluminum particles and bearingphase particles, more than 50 weight percent of said particlescomprising aluminum particles and the balance of said particles beingselected from said first and second groups of additives, the bearingphase material of said sacrificial layer having an interstitial positionrelative to said aluminum particles.
 2. A fine dispersion aluminum basemulti-layer bearing material comprising:a. the sintered coherentmulti-layer composite of claim 1; and b. a steel backing layer directlybonded in face-to-face relationship to said bonding layer of saidmulti-layer composite.
 3. A bearing strip according to claim 2, whereinsaid sacrificial layer consists essentially of 20% tin, 1% copper andthe balance aluminum.
 4. A bearing strip according to claim 2, whereinsaid sacrificial layer consists essentially of 20% lead and the balancealuminum.
 5. A bearing strip according to claim 2, wherein saidsacrificial layer consists essentially of 17% lead, 3% tin and thebalance aluminum.
 6. The fine dispersion aluminum base multi-layerbearing material of claim 2 wherein said powder metal bearing layerconsists essentially of about 100% prealloyed particles.
 7. The finedispersion aluminum base multi-layer bearing material of claim 2 whereinsaid bearing phase material of said powder metal bearing layer compriseslead.
 8. The fine dispersion aluminum base multi-layer bearing materialof claim 2 wherein said powder metal bearing layer consists essentiallyof 8.5% lead, 1.5% tin, 4% silicon, 1% copper and the balance aluminum.9. The fine dispersion aluminum base multi-layer bearing material ofclaim 2 wherein said powder metal bearing layer consists essentially of17% lead, 3% tin, 1% copper and the balance aluminum.
 10. The finedispersion aluminum base multi-layer bearing material of claim 2 whereinsaid powder metal bearing layer consists essentially of 20% tin, 1%copper and the balance aluminum.
 11. A fine dispersion aluminum basebearing strip comprising:a sintered, coherent powder metal bonding layerconsisting essentially of more than 55 weight percent aluminum and thebalance selected from a first group of additives consisting of silicon,copper, manganese, magnesium, nickel, iron, zinc, chromium, zirconium,titanium and mixtures thereof; and a sintered, coherent powder metalbearing layer on said bonding layer, said bearing layer consistingessentially of at least 55 weight percent aluminum and the balanceselected from said first group of materials in an amount of 0 to about20 weight percent and from a second group composed of bearing phasematerials in the amount of about 5 to 25 weight percent, said secondgroup consisting of lead, tin, cadmium, bismuth, antimony and mixturesthereof; at least all of said aluminum and said bearing phase materialof said bearing layer being in pre-alloyed particle form to establish anintra-particle position relative to each other, said powder metalbonding layer and said powder metal bearing layer being bonded to eachother by a sintered transition zone of compacted intermingled powderparticles of said bearing layer and said bonding layer.
 12. A finedispersion aluminum base multi-layer bearing material comprising:asintered, coherent, multi-layer powder metal composite comprising apowder metal bonding layer and a powder metal bearing layer stronglybonded to each other by a sintered transition zone of compacted,intermingled powder particles of said bearing layer and said bondinglayer; and a steel backing layer directly bonded in face-to-facerelationship to said bonding layer of said multi-layer composite; saidpowder metal bonding layer consisting essentially of more than 55 weightpercent aluminum and the balance material selected from the groupconsisting of silicon, copper, manganese, magnesium, nickel, iron, zinc,chromium, zirconium, titanium and mixtures thereof; and a sintered,coherent powder metal bearing layer on said bonding layer consistingessentially of at least 55 weight percent aluminum and the balanceselected from said first group of materials in an amount of 0 to about20 weight percent and from a second group composed of bearing phasematerials in the amount of about 5 to 25 weight percent, said secondgroup consisting of lead, tin, cadmium, bismuth, antimony and mixturesthereof; at least all of said aluminum and said bearing phase materialof said bearing layer being in pre-alloyed particle form to establish anintra-particle position relative to each other.
 13. A fine dispersionaluminum base bearing according to claim 12 wherein said powder metalbearing layer consists essentially of about 100 percent pre-alloyedparticles.
 14. A bearing according to claim 12, wherein said bondinglayer consists essentially of 6 percent silicon and the balancealuminum.
 15. A bearing according to claim 12, wherein said bondinglayer consists essentially of 0.8% silicon, 4.4% copper, 0.8% manganese,0.4% magnesium and the balance aluminum.
 16. A bearing according toclaim 12, wherein said bearing layer consists essentially of 8.5% lead,1.5% tin, 4% silicon, 1% copper and the balance aluminum.
 17. A bearingaccording to claim 12, wherein said bearing layer consists essentiallyof 17% lead, 3% tin, 1% copper and the balance aluminum.
 18. A bearingaccording to claim 12, wherein said bearing layer consists essentiallyof 20% tin, 1% copper and the balance aluminum.
 19. A bearing accordingto claim 12, wherein said bonding layer consists essentially of 100%aluminum of commercial quality, and said bearing layer consistsessentially of 8.5% lead, 1.5% tin, 4% silicon, 1% copper and thebalance aluminum.
 20. A bearing according to claim 12, wherein saidbonding layer consists essentially of 0.8% silicon, 0.4% copper, 0.8%manganese, 0.4% magnesium and the balance aluminum; and said bearinglayer consists essentially of 8.5% lead, 1.5% tin, 4% silicon, 1% copperand the balance aluminum.
 21. The fine dispersion aluminum basemulti-layer bearing material of claim 12 wherein said bearing phasematerial of said powder metal bearing layer comprises lead.